


Heat Wave

by SheeWolf85



Category: Undertale (Video Game)
Genre: Bara Sans, Cum Inflation, Cunnilingus, Ectobiology, F/M, Fellatio, Female Reader, Heat Fic, I Tried, Large Cock, Light BDSM, Monster Heat, Orgasm Delay, Orgasm Denial, Reader-Insert, Size Difference, Size Kink, Smol Reader, UF!Sans, Underfell, mafiafell
Language: English
Status: In-Progress
Published: 2018-11-18
Updated: 2018-11-17
Packaged: 2019-08-25 05:56:49
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,587
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16655497
Author URL: https://archiveofourown.org/users/SheeWolf85/pseuds/SheeWolf85
Summary: You and Sans, a powerful member of the Monster Mafia, have been dating for a few months now. He's been nothing but suave, charming, and a perfect gentleman, intent on respecting your boundaries.You'd like to shove those boundaries in the nearest lake and watch them drown.You're ready to take the next step in your relationship, but Sans seems to be oblivious. Maybe it has something to do with all the unwanted advice and warnings you've been getting about what might happen when Sans goes into heat. You don't care. You love him. You want him. You know he wants you. You're going to have him.





	Heat Wave

**Author's Note:**

  * For [malenchka](https://archiveofourown.org/users/malenchka/gifts).



> For Malenchka, first place winner of my 200 follower fic raffle on Tumblr! 
> 
> I seriously have no fucking clue what to call this, so you get that horrible title.
> 
> This first chapter only covers a few of your requested kinks, and I promise you'll see more in chapter 2. My love of backstories couldn't just write a fucking heat fic and leave it at that, so you get introductory sex before the main event. 
> 
> I apologize in advance for my terrible attempt at writing MafiaFell Sans. I really did try. I even read some MafiaFell stories...what I could find, anyway. There's an appallingly small amount out there. I do love him; he's a sexy motherfucker. I just can't write him all that well.
> 
> Anyhow, I hope you enjoy this, and chapter two will hopefully be out before the next century is over. I have it all planned out, it's just getting the time to write uninterrupted that's the hard part these days!

Soft lights twinkled all around you as you took your skeleton boyfriend’s large hand and let him lead you out onto the dance floor. His other hand went to your hip and gently pulled you into him. You looked up at him as you began to move, dancing slowly to the sweet love song playing.

“you really do look perfect tonight, dollface,” Sans muttered, his deep voice just this side of a growl.

You couldn’t help but blush. He’d picked out your dress, stating that he just had to see you in it. It reminded you of Jessica Rabbit’s dress, and he may have done that on purpose. Either way, it was long, red, and sparkly, and it fit you like it had been tailored to your body. It really wouldn’t have surprised you if he’d somehow gotten your measurements to do just that. The top clung to your breasts seemingly by magic and the back dipped nearly down to your hips.

You’d had help getting ready that evening, at his insistence. Your hair had been pulled up into some kind of elegant updo you’d never be able to manage on your own, and your makeup had been done to smoky perfection.

“Thank you; you do too.” You smiled up at him before looking him over.

He was dressed impeccably in a suit that had undoubtedly been tailored to him. All of his clothes had to be; it was basically a miracle if he found something off the rack that fit him properly. Tonight, he wore black slacks with shiny black dress shoes, a silky white button-up, and a gray vest. He’d removed the black jacket he wore over the top almost immediately, stating the place was too hot to wear it.

Not like you really minded much; you liked to look at him in anything he chose to wore.

As you looked him over, you thought about what this night represented for you. It was your six month anniversary of when you’d begun dating, and he’d insisted that any girlfriend of his deserved nothing but the best.

You’d first met Sans roughly a year ago. You’d like to say that the unforgettable circumstances in which you met him meant that you’d be able to remember the actual day it happened, but that was too much to ask for.

You and a few friends had been bar-hopping that night, and for shits and giggles you decided to try out the monster bar on the other side of town. Neither you or any of your friends had anything against monsters, but you knew a lot of them dealt in mob activities and could be a bit more dangerous than most humans you might encounter. That thought didn’t deter you from going against what should have been common sense.

It just so happened that night was one that a few drug traffickers tried to pull off a switch in Grillby’s bar. Not only did Grillby take offense to that, but he’d called in backup.

You would like to say that you were intimidated by the huge, gruff skeleton who came in and gave the bad guys a reason to run, but in reality, you were in awe.  The guy had to be close to seven feet tall and the way he dressed told you he was an important figure in the mafia. Not to mention his razor sharp teeth, one of them a bright golden color that somehow made him appear even more menacing. Better not to mess with a guy like that, right?

Not that it was your fault, but you still couldn’t regret a single thing that had happened. One of the drug traffickers had pulled you out of your seat, using you as a hostage. It had been an insanely bad idea. For whatever reason, the mobster took offense to you being used as a shield.

His left eye glowed with a bright red iris just as a few sharpened bones materialized out of thin air. You didn’t even have time to scream before one of the bones shot forward and impaled the man holding you in the head. His hand holding the knife had slowly fallen down to his side before he slumped down to the ground. Your friends had pulled you out of the way and to safety while the mobster took care of the rest of the traffickers.

“you okay?”

Sans’s voice pulled you back from your memories. You looked up at him again and nodded.

“Just thinking about how we met. It’s been a year; can you believe that?”

His large hands on your back pulled you in a little tighter as he leaned his head down to kiss your forehead. “feels like i’ve known you all my life.”

You couldn’t help but blush again. He sure knew how to lay on the charm. You leaned in and rested your head on his chest. Even in your heels, the top of your head barely managed to reach his shoulders.

You’d figured out pretty quickly that part of the reason he’d been so pissed off about you being a hostage was that he thought you were a kid. He didn’t stop to wonder why a human kid would be in Grillby’s bar; he’d just acted on instinct. After the drug traffickers had been dealt with, he came over to you to check on you. It wasn’t your fault you were so short. Your small stature made people think you looked like a twelve-year-old, despite the fact that your curves were far more adult than any twelve-year-old you’d seen recently. It had taken actually showing him your driver’s license to get him to believe you were adult. Even then, he seemed a bit skeptical.

Your friends all seemed to be scared of him, though you couldn’t fathom why. Not only had he just saved your life, but there was something about him that emanated warmth and comfort. He’d stayed that night until you and your friends decided to leave, and you knew it wasn’t just your imagination when you caught him staring at you.

You also knew it wasn’t a coincidence when you ran into him at the store a few days later. You’d been minding your own business, shopping for weekly groceries, when you literally ran right into him. He pretended to be surprised to see you, but it was so painfully obvious that he’d been following you. You had decided not to say anything, just to see how deep he’d dig himself before you finally let on that you knew.

You “spontaneously” bumped into him weekly after that. You asked him if he’d moved to this side of town, and he’d denied it. You asked him why he was even on your side of town, and he’d shrugged, not offering much of an explanation other than that he went wherever the fuck he wanted to go.

Meeting up with Sans had become your favorite part of the week. You loved spending time with him, even if it was only for a few minutes. Occasionally, he’d find some reason to stick around for a few hours. You never questioned him, knowing it would not only be useless, but also that you enjoyed his company.

There had been two weeks in a row that you hadn’t seen him, and you’d gotten nervous that he was bored with you. When he came back and you asked him about it, he’d flustered only for a second before he gave you his signature lazy-yet-sure-of-himself grin and explained that he had a personal problem to take care of.

Then one day he’d asked you out. Your heart had fluttered a little before you accepted. Over the next six months, he’d shown you the grand side of mafia life and protected you from the dangers of mafia life. He was sweet as hell and always courteous of your boundaries.

Month by month, you grew closer to him. You began to notice certain changes in him. He never said anything—continued to be as suave and gentlemanly as ever—but something about the way he looked at you and touched you said that he wanted to take this relationship further.

You weren’t sure how a physical relationship would work with a monster like Sans, but you were eager to find out.

After you’d first started dating him, you began to get unsolicited comments about the dangers of dating a monster. The majority of those comments revolved around Sans going into heat.

_“He won’t take no for an answer when he’s in heat,”_ one person had said.

_“They’re like animals; all he’ll want is sex,”_ another had warned.

Deep inside, you weren’t really sure that one bothered you.

_“He won’t care if it hurts; he won’t stop until you’re pregnant.”_

That one was a little worrisome, but only because you weren’t sure how monster-human babies worked. Although there had been monster-human couples before you and Sans, none of them had ever conceived.

Regardless of the warnings you received, you didn’t bother to bring up heats to Sans. You figured if it was actually a dangerous thing, he’d talk to you about it. He’d warn you. You trusted him.

You pulled back and looked up at him again. “Thank you for this, Sans. It’s been a really wonderful evening.”

He grinned and held you just a little tighter. “it’s been my pleasure, cupcake. i’m the one who gets to kiss the most beautiful woman in the world at the end of the night.”

You smiled softly. “Why wait?”

His grin softened as he leaned down and kissed your lips. You’d explored a few things with Sans; kissing, soft touches, and some basic exploring underneath clothing. He’d always stopped you before anything went any further, stating that he didn’t want to push you too far. Sometimes it was annoying, but you didn’t want to push him either, so you accepted it when he’d pull back.

Tonight, however, you had different plans. You were going to invite him inside when he took you back to your apartment, and you were going to do your best to seduce him. You wanted him, and you knew he wanted you, too.

At the end of the dance, he twirled you and dipped you, then led you back to your seat.

At the end of the night, Sans opened the back door of the car for you to slip into he seat. He got in beside you and instructed his driver to take you home. You spent the ride thinking over how you were going to invite him in. Did you want to be direct and let him know you wanted to sex him up, or did you want to be coy about it?

You ran out of time as the car pulled up to your house. Sans got out and opened your door for you, then walked you to your door.

“i had a real great time tonight, doll,” he said gruffly. His eye lights danced down your form as his hands smoothly caressed your arms.

Your body was on fire as he leaned down to kiss you. As he pulled back, you gripped his shirt and smiled your best sexy smile.

“Do you want to come in?”

His eye lights shrunk, a sign that he was either pissed off or turned on. Hopefully the latter.  He pulled you in a little tighter and kissed you deeply for a moment before he pulled back and hugged you to his chest.

“sure you wanna invite me in?” he asked, dipping his head so you felt his breath in your hair.

You pulled back just enough to look up at him through your lashes. “I’m very sure.” You skimmed your fingers down the fine silk of his shirt, putting enough pressure to feel his ribs underneath. You felt him shiver as he nodded.

As you turned to unlock the door, he sent a gesture to his driver. You saw the car pull away just before Sans all but slammed the door shut behind him. You really hoped that meant he intended the stay the whole night with you.

Once the door shut, Sans pulled you up close and bent down to claim your lips in a deep kiss. Your hands gripped his shirt tightly, attempting to pull him even closer as you sucked his tongue and pressed your body into his.  His hands began to wander, one sliding up your neck to settle at the back of your head and the other going down to grip your ass tightly.

He pulled back a moment later, his face flushed with red magic. “babydoll, i want you so fucking badly,” he ground out, his hand on your ass squeezing.

You nodded and leaned into him to kiss his jaw. “I want you, too. Come on.”  You stepped back, a little disappointed when his hands slipped away from you, but he followed as you walked to your bedroom.  Once inside, you shut the door and pressed your back against it. You watched him as he stood in the middle of the room, looking around as if it was the first time he’d ever been there.

“i don’t wanna hurtcha,” he confessed, his voice softer than you’d ever heard it before. “yer so fuckin’ tiny…”

You blushed and walked up to him, reaching up to put a hand on his cheekbone. “I’m also horny, baby; I promise I can take it.”

His eye lights seemed to darken then, and his hands shot out to grab you by the waist. He pulled you in and kissed you hard as his hands began teasing the sides of your chest where the dress was held in place by fabric tape. You let him pull it free and shivered as the dress fell to your feet.

The monster that had helped you get ready earlier wouldn’t allow you to wear anything under the dress. They’d said that a bra was out of the question for obvious reasons and underwear would leave panty lines. You hadn’t argued too hard, knowing you’d be with your big, strong protector should you have a wardrobe malfunction.

You stood in front of him naked, his bony hands sliding smoothly over your body. The rings he wore were warm against your skin and caused you to shiver as he gripped your right ass cheek.

“yer so fuckin’ sexy, baby,” he growled. His hand not on your ass slid up your front to fondle your breasts. “can’t believe how fuckin’ lucky i am.”

You smiled as you stepped out of your heels, kicking them to the side, and ran your hands up his chest. “I think I’m the lucky one,” you cooed. “Though, you are way too overdressed at the moment.”  You began to unbutton his shirt, and he let you.

Once off, he grinned. “pants ain’t gonna unbutton themselves.”

You gave him a look even as your hands settled on his belt buckle. “No, I guess they won’t.”  You leaned in and kissed his sternum, let your tongue graze along crisscrossed scars, as you unbuckled his pants and let them fall to the floor.

He stepped out of his pants and shoes at the same time, then took a moment to take off his various rings and set them down on the table beside your bed. As he set the last one down, he winked at you.

“don’t wanna risk losin’ one’a them inside ya.”

Your whole body flushed with desire at his words.  He came up to you again and kissed you as he urged you back toward your bed. You laid down on your back and watched with delight as he laid next to you. He kissed you deeply as his hand wandered down your stomach, not stopping until he cupped your pussy and applied slight pressure to your clit.

You moaned and pressed your hips up into the touch. His hand began circling, spreading your wetness around until he could easily massage your clit. Your hands clung to his ribs as you cried out, bucking your hips in time to his movements.

“Fuck, Sans…Oh, baby this feels good.”

He smirked at you and kissed your cheek. “yer so fuckin’ hot right now, dollface. you like this?”

You nodded eagerly. “Oh, yes!”

He pressed a finger inside you, twisting and pumping delightfully for a few moments before he added another. His thumb began circling your clit, causing you to cry out and buck your hips without rhythm. “you gonna cum?”

Your whole body warmed again, and you nodded. “Yes…God, yes!”

Then his hand was gone. “no, not yet.”

You whimpered. “But…”

He smirked and kissed you again. “not ‘til my cock is buried in that cunt, sweetheart.”

You shivered. “Please, Sans! _Please_ _fuck me_.”

Sans chuckled and moved over you, straddling your legs. You looked at him helplessly as he took your wrists in one hand and pulled them above your head.

“i will, cupcake. i will. keep your hands here.”

Your fingers gripped the pillow beneath your head as you nodded.  He leaned down and kissed your neck, and you moaned.

He took his time moving down your body, kissing and nipping as he did. As turned on as you were, you felt your orgasm slipping further away. A little disgruntled yet trusting him completely, you let him spread your legs as he settled his face between them.

He licked your pussy once and groaned. “fuckin’ tasty cunt.” He licked you again, then once more before he flicked his tongue across your clit, holding your lips apart with his fingers.

Your hips bucked wildly against his face as you cried out. You desperately wanted to reach down to touch him, but you kept your hands where he’d put them, gripping the pillow hard enough your fingers ached.

Just as you felt your orgasm building again, he stopped and pulled back. He wiped his face with the back of his hand and grinned at you.

“Sans, please…I was so close!”

He nodded and leaned over you again, kissing your lower belly. “i know, sweetheart. not ‘til you can cum on my cock.”

He kissed his way back up your body, stopping for a moment to lick and nip at your nipples. You could feel his cock, thick and heavy against your thigh. You looked down curiously and shivered; like the rest of him, it was fucking huge. You couldn’t wait to get it inside you.

A little deviously, you began moving your leg to rub against his dick. He groaned and moved up a little more, licking your throat before biting down gently.

“Come on, Sans!” you whined.

He kissed your throat again before moving to your lips. “you ready, sweetheart?”

You nodded. “Yes. God, yes!”

He kissed you again as he put himself into position. You gasped as he pushed in slowly, your body already so turned on and ready that it was nothing but pleasure. Inch by inch, your body was stretched until he’d hilted deep inside you.

“stars fucking dammit,” he panted against your skin. “yer fuckin’ tight, baby. you okay?”

“So good!” You tried to wrap your arms around him, but he caught your wrists and put them back above your head.

“don’t make me tie you up, babydoll.”

You shivered, thoroughly enjoying that idea. Maybe another time, though. This time, you just wanted to cum.

He finally began to move, pulling out only halfway before thrusting back in. He set a slow pace, allowing your body to fully get accustomed to his size before fucking you the way you knew he was dying to. His hands caressed your body as he swore against your hair, gradually increasing his pace until he was pounding into you. The bedsprings squealed in protest with each movement and the headboard slammed against the wall.

“fuck, baby,” he growled, deep. “ _fuck_ , your pussy is so tight!”

You cried out, your toes curling as your orgasm began to build. It tightened in your gut, and you wrapped your legs around him to hopefully keep him there. He had said you’d get to cum on his cock, and you weren’t about to let him take that back now.

“I’m gonna cum!” you wailed, arching your back into him. “Please let me cum!”

He kissed your ear and growled, “cum for me, sweetheart. cum on my cock.”

Your body seized up as your orgasm hit you hard. Your vision went white for a moment and everything but your release disappeared. As you came back down, you felt his cock throbbing inside you as he came, a steady growl coming from his chest.

As you both relaxed, you let your arms finally embrace him, holding him tightly to you.

“I really love you, Sans,” you whimpered.

He kissed your cheek. “love you too, dollface.”  He shifted to lay beside you and pulled you up to him. You curled into his side and kissed his ribs.

“That was incredible.”

He chuckled. “yeah, not bad for our first time.”

It earned him a smack to his sternum, but he only laughed harder. You couldn’t help but smile; you knew he’d enjoyed himself as much as you had.

“You’re going to stay with me, right?”  You looked up at him.

His smile was peaceful. “ain’t gonna fuck ya and leave ya, sweetheart. i do gotta leave in the mornin’, but i’m stayin’ here ‘til then.”

You grinned and stretched up enough to kiss his teeth.


End file.
